The present invention relates to a mechanism for reciprocating machine parts such as a carrier of the print elements in a matrix line printer. More particularly, the invention relates to oscillating a print element carrier moving parallel to a platen element in forward and reverse passes and being connected to a drive which basically provides a rotating motion.
Oscillating shuttle mechanisms generally cooperate with an object which extends along the shuttle path and are provided for treatment, processing, observing, measuring or working whereby particularly the shuttle is to move along a particular path and in accordance with a particular velocity profile determined by a particular set of parameters. Related thereto in general are devices in which a work medium, tool, instrument, actuator or the like is to be operated in dependence upon a particular displacement or position. Open loop operation is desirable in this case in order to avoid complex position monitors and transducers as inputs for feedback circuits.
The print element carrier in a matrix line printer requires an operating system which permits the carrier to run at a constant speed over certain displacement path portions or increments and printing requires also position dependent operation. Generally speaking, the print elements on the carrier are constructed to print dots and they are configured, for example, as hammer tips or the tips of wires. These elements are mounted on the carrier particularly so that the respective tips are arranged along a particular line which could be termed horizontal, although the overall position of the printer is generally, or should be independent from such absolute orientation. This horizontal line extends transversely to the direction of the print medium (paper) upon which dots are being printed. During print passes the hammers or wires, i.e., the print element carrier reciprocate back and forth along that horizontal line. The elements themselves are actuated, i.e. caused to advance toward the print element in a direction which is transverse to both the print medium advance and the direction of shuttle reciprocation.
The print elements are actuated individually for purposes of printing to thereby obtain their advance. They are actuated when the shuttle has reached particular predetermined relative positions along the line of reciprocating displacement. Time and position dependent actuation and operation is critical in terms of accuracy because it reflects directly the quality and appearance of the printed characters. Of course, the power and speed of the printer depends on high speed operation in all instances. Obviously a high speed is required if such a printer is an output device in an electronic data processing system.
A shuttle mechanism is disclosed in European Pat. No. 44415 and being comprised essentially of elliptical gears oriented in particular phases in relation to each other. In order to simulate similar motion and displacements, particularly contoured cams or cam shafts have been suggested as an alternative. Also, shuttle mechanisms have been constructed using electromagnetic, i.e. electroinductively operating linear motors. A further approach includes feedback controlled drive motors for the shuttle and print element carrier.
Particularly contoured cams or camshafts are disadvantaged by very high accuracy and tolerance requirements during manufacturing. Detrimental is that the accuracy of operation requires intimate engagement of operating parts with particularly contoured cam surfaces which inevitably produces considerable wear resulting in a relatively short life. Positive connections, however, are not suitable for higher speeds. Linear motors, electromagnetic coils or controlled motors are disadvantaged by the high expenditure that is required to obtain the requisite control. Moreover, these motors consume a considerable amount of power and due to the particular operating mode they have a rather low efficiency while occupying a considerable amount of space.